An imaging detector of radiation includes a number of pixels and converts the intensity or energy of incident radiation into a count value inside thereof. Then, the result of count can be extracted to outside by various kinds of measures.
In the example shown in FIG. 2 of Patent Document 1, charges in proportion to the amount of energy output from the photodiode by incident X-rays are input to the charge amplifier circuit. Then, only incident signals corresponding to energy higher than a certain reference voltage are turned to pulses, which are input to a counter and counted. The count is read by the 10-bit data path. When performing read, it is necessary to send a signal one by one into the read circuit from outside and to send out data of the counter to the path.
The problem of this system lies in that a read signal corresponding to each of all the read circuits is necessary. Because of this, it is necessary to provide a number of internal signal lines or to adopt a system in which a numerical value is specified as an address and the numerical value is decoded. With the former, the circuit becomes complicated and with the latter, a demerit that time necessary for read is increased arises.
In the example of FIG. 4 of Patent Document 1, the counter is connected to the neighboring read circuits on both sides continuously with 1-bit data width in between and data is sent out sequentially at the time of read. Due to this, compared to the example of FIG. 2, the circuit configuration is simplified remarkably. In this case, but, it is necessary to read the data of all bits that all the read circuits have, and therefore, it takes time to read data according to the configuration of the imaging device. Due to this, the frame rate is restricted by the read time.
In the example of FIG. 2, by limiting the number of read circuits to be read, it is also possible to reduce the amount of data itself and to shorten the time necessary for read. In this case, however, data to be configured as an image is lost at a specific portion, and therefore, there is a possibility that information that should be possessed as image data is lost remarkably.
In Patent Document 2, a reading method adopting another system is shown (FIG. 5, FIG. 6). Here, data counted by the asynchronous n-bit counter is temporarily moved to the loadable shift register and the shift register is connected in series to the previous pixel and the next pixel continuously. With this configuration, it is possible for the counter to start the next counting operation immediately by temporarily moving the data to the shift register. However, unless all the data of the shift register is read, it is not possible to move data from the next counter to the shift register, and therefore, the frame rate is restricted by the time taken by read from the shift register.
In Patent Document 3, as another example, the method is shown (FIG. 6), in which data is read by specifying the position by the ROW specification and the COLUMN specification for the read cells arranged on the imaging device in the form of a matrix. In this case, the read time is determined by [number of times of read of all the read circuits]×[number of bits of each piece of data]. Further, similar to the example of FIG. 2 of Patent Document 1, if the number of read circuits to be read is limited, information that should be possessed as image data is lost.
Patent Document 1: U.S. Pat. No. 7,586,168
Patent Document 2: Japanese Patent Publication No. 2001-502424
Patent Document 3: U.S. Pat. No. 7,514,688